Is working memory a necessary and sufficient model for explaining conscious awareness?

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Leandro Castelluccio

 

One of the biggest challenges of current research in neuroscience is to explain how conscious awareness arises from brain function. One interesting idea about this area emerges when we consider another phenomenon: working memory. It seems common sense that everything that we are aware of at the present moment is part of our working memory, it is an active content of it that we can explicitly report and use to guide our behaviour. As Baars and Franklin (2003) point out, an important observation that can be made from the research into working memory, is that all active components of classical working memory are conscious, these refer to things such as input, rehearsal, visuospatial operations, recall and report. According to the authors, this fact would suggest in effect that conscious experiences play a key role in classical working memory. Or we could say that working memory plays a key role in giving rise to conscious awareness.

One fact that could support the above is that working memory and conscious perception share common neuronal substrates (Soto and Silvanto, 2014), suggesting that they are tightly coupled, particularly the prefrontal cortex and the connections to parietal areas has been associated to conscious states forming a global neural workspace for conscious accessibility of information, which in turn has been linked with working memory operations and cognitive control. Baars (1997), for example, talks about the “global workspace”, which implies a subjectively experienced event that is part of the working memory.

Hassin, Bargh, Engell and McCulloch, (2009) addressing Baddeley`s model about this subject, explain the progression of considering that a subset of the information that is actively maintained in working memory is that of which we are aware of, to suggesting that conscious awareness could be one of the functions of the central executive component of working memory. Recently, it has been proposed that awareness is inherent in the interaction between the executive and the episodic buffer. According to Baddeley (2000), this episodic buffer, comprises a limited capacity system, which provides temporary storage of information held in a multimodal code that has the capacity of integrating information from the subsidiary systems, and also from long-term memory, to form a unitary episodic representation, where conscious awareness would be the main mode of retrieval from this buffer. The idea of an episodic buffer that stores information in a multimodal code, binding it from the subsidiary systems, is appealing for explaining, for example, our sense of a unified and integrated conscious experience, where different sensations and qualia manifest together as a whole. There could be, therefore, an important role of working memory in conscious awareness.

There is a problem, however, that needs to be addressed before we talk about this relationship, which is the problem of defining conscious awareness. There does not seem to be a consensus about what the term “consciousness” means. Wilkes (1984) has argued in connection with this, that the term “consciousness” is like the word “thing”, which is useful to designate many elements because it lacks specific content. And indeed “consciousness” has been used with a great variety of meanings, even the so called “theories of consciousness” have a very diverse intellectual structure (Lycan, 2006). This is a problem when we try to find the neural correlates of consciousness, if we are talking about different things, then it is hard to compare what different authors have found about brain function and consciousness, needless to say, that it would be even more difficult to address the issue of consciousness and its relation to something else, as in this case: working memory.

The specific meaning that I would like to use here is that of quale (or qualia in plural form). Qualia refer to the subjective sensations or experiences of things, for example, the experience of redness when one perceives something of that colour. (Blackmore, 2005). It is that which I think we can relate the most when we talk about being conscious about something or having conscious awareness, therefore it seems the proper meaning of the term to use and to discuss the neural correlates and relationships to other phenomenon.

Ramachandran and Hirstein (1997) talk about certain laws that must be present in order to have qualia (conscious awareness of things). Of importance to our discussion are the second and third law, which indicate that qualia can be used for other processes, and that the subjective experience must remain for a certain amount of time (which would imply memory), so that the executive processes can work with that content. This is very interesting when we consider our topic, since working memory would be implicated in these two laws, which would support the idea that working memory is necessary for quale or conscious awareness.

One piece of evidence supporting the idea that memory contributes to conscious awareness comes from the phenomenon of blidsight. This refers to the condition in which subjects are capable of discriminating certain visual information without being conscious of what they are observing (Weiskrantz, 1986). According to Milner and Goodale (1995), patients with blindsight can do things such as correctly rotate an envelope and place it on a box which is either in a vertical or horizontal position, even though they cannot consciously perceive the box’s orientation in space. It is argued that the dorsal visual stream which process information related to the orientation of objects in space and affects the movement of the arm works as a sort of reflex, with ongoing information that it is not retained (there is no memory), and once the information is gone it cannot be used for other processes, failing to fulfil the second and third law of qualia, which would explain why there is no conscious awareness in these cases (Ramachandran and Hirstein, 1997). Like we mentioned before, according to these authors, memory and the possibility to work with the information is necessary for conscious awareness.

Crick and Koch (1992), have stated that there might be particular neurons associated to qualia, and this neurons would be those that project to the frontal lobes. If we take into account the role of the frontal lobes in decision making and working memory (Gazzaniga, Ivry and Mangun, 2013), this would make sense when we think about the laws of qualia. Working memory has neuronal correlates in frontal lobe activity. For example, when we analyze visual working memory encoding, several cortical and subcortical regions appear to activate, and it has been found that the lateral prefrontal cortex (the inferior frontal junction) shows a temporal activation profile associated with the duration of encoding. This region corresponds to the prefrontal area previously implicated in “attentional blink”, suggesting that this region is highly involved in visual working memory encoding (Todd, Han, Harrison, and Marois, 2011). Also, in an experiment conducted to examine what brain regions are commonly and differently active during various working memory tasks, a widespread bilateral fronto-parietal network activation was observed. Several regions were sensitive to specific task components, like Broca’s region during verbal tasks or ventral premotor cortex for object identity and dorsal premotor cortex for object location. At the same time, a consistent “core” network emerged from conjunctions across analyses of specific task designs and contrasts, involving regions which are necessary during working memory task (Rottschy, Langner, Dogan, Reetz, Laird, Schulz, . . . Eickhoff, 2012). Additionally, Naci, Cusack, Owen and Anello (2014) identified what it appears to be a common neural code that underpins similar conscious experiences, consisting of synchronized brain activity across frontal and parietal cortices in regions known to support executive function. So it appears that there is a relationship between conscious awareness and memory and executive function, supporting the validity, in terms of neural correlates, of the necessity of the two laws of qualia previously mentioned for conscious experience to happen.

There are, however, several critics towards the conclusions that have been stated about blindsight and what it means for consciousness, so we should be cautious if we are using this case as supporting evidence for saying that memory, for example, is necessary for conscious awareness. Weiskrantz (2009) has asked whether blindsight is not in fact a degraded form of normal visual function, and it is questioned whether there is a truly separation between the dorsal and ventral stream of visual processing in blindsight and in general (Himmelbach y Karnath, 2005; Schenk y McIntosh, 2010).

Soto, Mäntylä, and Silvanto (2011) indicate that current understanding shows that the encoding of information in working memory, maintenance, retrieval and use in decision making of working memory operates on the contents of consciousness. However, Soto and Silvanto (2014) analyze the question of whether awareness is mandatory for the operation of working memory and also that the contents of working memory are necessarily associated to conscious states that can be reported. It appears that we are not necessary aware of engaging in working memory operations. According to these authors, no evidence of participants in an experiment being aware of having extracted the sequence information in a task was present. It seems that extracting the spatial sequence information to guide behaviour requires maintenance and updating of memory representations, and so it is concluded that there were operations without intentional orientation and awareness of those operations. At the same time, recent studies have examined how introspection of working memory contents and the actual working memory accuracy are affected by the presentation of distracters. Evidence suggests that working memory accuracy is impaired by either conscious and nonconscious distracters that are highly dissimilar from the working memory content, and that subjective vividness ratings of the working memory content is reduced both by similar and dissimilar distracters but only when they were non-conscious, which would suggest that these contents are malleable by factors not influencing the actual working accuracy. (Soto and Silvanto, 2014). This would indicate that unconscious processes take part and influence working memory.

It seems that working memory can indeed operate on non-conscious information, as shown by the fact that observers can maintain unseen, masked, visual cues, filled with similar distracters and still perform significantly above chance level, during a delayed discrimination test. High level cognitive functions, such as arithmetic computations and reading, can be carried out over nonconscious information. These would fall within the repertoire of working memory functions, and depend on the availability of the executive component of it (Soto and Silvanto, 2014). These authors argue that it is likely for what we call working memory to be formed by different types of mechanisms, and these various mechanisms may constitute distinct working memory types with specific behavioural functions. We could say that some aspects of it are conscious and others are not.

Cognitive processes that are controlled are conventionally assumed to operate in a slow, effortful, and voluntary manner, it is assumed that such processes are conscious (Schmidt, Crump, Cheesman and Besner, 2007). However, as these authors notice, results of four experiments provide evidence for controlled processing in the absence of awareness. In this case, participants identified the colour of a neutral distracter word, showing that colour identification was faster when the words appeared in the colour they were most often presented in relative to when they appeared in another colour. This occurred even for participants who were subjectively unaware of any contingencies between the words and the colours. It appears that participants who were not aware of the relation between distracter words and colours could still control the impact of the word on performance depending on the nature of the previous trial. It was also found that the contingency effect does not depend on the level of awareness, thus ruling out explicit strategy accounts, all these proving that implicit control can exist.

According to Hassin, Bargh, Engell and McCulloch (2009), it is suggested that when certain processes are not in our current conscious focus they are idle, that is, they do not do any work. But it is a possibility that working memory can operate implicitly. Working memory can be recruited without conscious intention, which would be beneficial, in the sense that conscious content is limited, providing a wider availability of useful information that would affect behaviour. These unconscious aspect of working memory would include active maintenance of ordered information for relatively short periods of time, context-relevant updating of information and goal-relevant computations involving active representations, also rapid biasing of task-relevant cognitions and behaviours, in the service of currently pursued goals. It seems that the results of five studies show that a working memory task, consisting of the online extraction and application of patterns, occurred in the absence of intention and conscious awareness, suggesting that working memory can operate unintentionally and outside of conscious awareness (Hassin et al., 2009)

According to Marien, Custers, Hassin, Aarts and Smith (2012), results of 6 experiments show that subliminal activation of a socializing goal, or an idiosyncratic personal goal, or an academic goal, was able to harm participants’ performance on an executive function task. The effects were unique to executive control, and were similar when the goal was activated consciously. It appears that an unconscious goal occupied executive control to advance itself more strongly when the goal had personal value.

At the same time, Hsieh and Colas (2012) found that a moving object can still attract attention when presented subliminally, however, the dynamic trajectory of an object and its task-relevant predictive patterns may not be monitored and maintained in visual working memory.

If it is the case that our working memory maintains content that is not conscious and that can be used in other processes and get certain behavioural responses, then it would not be true that memory of certain information and its possibility of being used for planning and decision making, for example, is a sufficient condition for conscious awareness, as the evidence mentioned above shows, there is information maintained by our working memory that does not comply with the two laws of qualia previously mentioned.

Dutta, Shah, Silvanto, and Soto (2014), provide evidence of the neural correlates of these high-level cognitive tasks (like learning of complex item sequences, reading, arithmetic or delayed visual discrimination) operating on an unconscious level. They show that the dorsolateral and anterior prefrontal cortex can operate on non-conscious information in a way that seems different from automatic forms of sensorimotor priming that would support implicit working memory processes and higher-level cognitive function. They explain that visual stimuli below the threshold for conscious report can nevertheless be maintained and accessed for later use in a delayed memory discrimination test. The prefrontal cortex role in working memory may not be restricted to visible items, for example, but may also extend to non-conscious processes in the service of visual working memory.

It appears that there are other processes going on that contribute to the particular subjective experience we have of things, we would conclude that more than working memory is needed for conscious awareness. For example, according to Northoff (2003), the qualitative, phenomenological nature of qualia, could be related to an early activation of the ventromedial prefrontal cortex. At the same time, the co-activation in the ventromedial prefrontal cortex and hypothalamus, and the deactivation in the ventrolateral prefrontal cortex and posterior cingulate cortex, might account for the experience of presence of qualia, referring to the idea that something like the sweetness of chocolate is experienced as absent of time. At the same time, Northoff (2003) indicates, for example, that the non-structural homogeneity (the experience of unity and wholeness of our sensations) could be related to the multimodal nature of the ventromedial prefrontal cortex, integrating different aspects of our experience. The notion of transparency of our experience, the idea that our sensation are part of the world and we have a direct contact with it, might be related to a reciprocal suppression between the ventromedial and ventrolateral prefrontal cortex.

From all this information we could conclude that conscious awareness might need working memory but not all working memory content might fall under the realm of the conscious. So it might be the case that working memory is a good model and a necessary one to explain conscious awareness, but not a sufficient one. Further research on this topic should focus, if it is possible, on whether there can be conscious awareness without any sort of working memory, which would address the question of working memory being necessary for conscious awareness.

References:

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